Method of concentrating phosphates from their ores

ABSTRACT

The present invention relates to a phosphate ore beneficiation process, which includes a method to float inadequately de-oiled phosphate particles prior to silica flotation. It is emphasized that this abstract is being provided to comply with the rule requiring an abstract that will allow examiners and searchers to quickly ascertain the subject matter of the technical disclosures. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims, as promised by the Patent Office&#39;s Rule 1.72(b) for abstracts.

The present invention relates to a phosphate ore flotation process. Theinvention modifies the commonly used “double float” process. In thedouble float process, the first float is to reject most of the silica byfloating the phosphate, producing a rougher phosphate concentrate, andthe second float is to remove most of the remaining silica in therougher concentrate by floating the silica. To prevent the phosphatefrom floating with the silica, the rougher concentrate is scrubbed withdilute acid prior to the second float. This process is referred to as“de-oiling”. The present invention includes a method to floatinadequately de-oiled phosphate particles prior to silica flotation,using a cationic collector.

The invention comprises the features that will be exemplified in thedescription hereinafter set forth, and the scope of the invention willbe indicated in the claims. In the drawing illustrating an embodiment ofthe present invention:

FIG. 1 is a schematic process flowsheet of the present invention; theinadequately de-oiled phosphate is floated in flotation device 70;

FIG. 2 is an example illustrating the relationship between cationiccollector dosage and the amount floated; and

FIG. 3 is an example illustrating the relationship between cationiccollector dosage and float grade.

From FIGS. 2 and 3, the cationic collector dosage needed to obtainoptimum or desired recovery and concentrate grade can be determined.

Referring now to the embodiment shown in FIG. 1, the phosphate flotationmethod of the present invention is shown and denoted generally as 10.

A flotation feed, constituting a phosphate ore rock slurry of −16 to+150 mesh size phosphate rock particles which is obtained from adesliming circuit of a phosphate beneficiation process (not shown), isintroduced into conditioning chamber 28 via line 20. A pH modifier andanionic reagents (collectors) such as a fatty acid soap and fuel oil,are introduced into chamber 28 via line 27. The pH modifier may becomprised of caustic soda, soda ash or ammonia. Other pH modifiers knownin the art for application to phosphate rock slurries may also be used.Petroleum sulfonates and other surfactants known in the art plusadditional water may also be introduced into chamber 28.

The slurry containing hydrophobic phosphate rock particles is removedfrom chamber 28 and introduced into a first froth flotation device 32via line 21 under conditions sufficient to float the hydrophobicphosphate particles to the top of the cells 33 as air is bubbled intothe cells. The froth (rougher phosphate concentrate) 48 are removed fromthe upper part of device 32 via line 49. The hydrophillic material 45,constituting mostly silica/sand particles remain in the water and sinkto the lower part of flotation device 32 and removed from device 32 vialine 46 for disposal by means known in the art (not shown). Theflotation device may comprise one or more cells 33 of conventional typeswhere air is introduced into device 32 by means of line 44.

In the first froth flotation circuit (rougher flotation circuit), thesilica content is reduced from 50-80 percent to 15-30 percent. Thephosphate ore is preconditioned with, for example, a fatty acid soap,which is preferentially adsorbed by the phosphate particles, causing thephosphate particles to become hydrophobic. When the hydrophobicphosphate particles are introduced into the flotation device thephosphate particles attach to the air bubbles and float. Most of thesilica particles remain in the water and sink. The floated phosphate ore(rougher phosphate concentrate) must be freed of collector before beingfed to the amine circuit to float most of the remaining silica. To dothis, the rougher phosphate concentrate is scrubbed with preferably adilute sulfuric acid (H₂SO₄) at a pH of about 2.5 to about 4.0, followedby rinsing with water. This process is referred to as de-oiling.

The de-oiling process is very critical to phosphate recovery. Inadequatede-oiling ultimately causes phosphate loss unless proper steps are takento reduce this loss. Inadequate de-oiling is usually a result ofinsufficient scrubbing and/or the use of an insufficient amount ofsulfuric acid. One way to overcome this problem is to simply add moresulfuric acid. The addition of more sulfuric acid, however, not onlyincreases cost, it may dissolve the phosphate and produce gypsum withthe subsequent loss of the dissolved phosphate to the V box overflow, asmore fully described herein below. Accordingly, heretofore sulfuric acidusage has been constantly monitored to obtain adequate de-oiling atminimum usage.

This monitoring is typically conducted by a plant operator's visualobservation of the flotation of phosphate in the V-box or in the aminecircuit. Generally, if no flotation of phosphate is visible an attemptis made to reduce the sulfuric acid usage. Alternatively, when theflotation of phosphate is visible sulfuric acid usage is increased. Whenpoor de-oiling occurs several minutes lapse between the initiation ofcorrective action by the operator and the process reaching steady state.In the mean time, phosphate floats and is lost to the amine tailings,which can significantly reduce phosphate recovery.

Maintaining a proper balance between optimum de-oiling and minimumsulfuric acid usage is a difficult task to achieve because the requiredamounts of sulfuric acid vary depending upon the chemical and physicalnature of the phosphate rock. In addition, these properties may changefrom one deposit to another. Further, the required amounts of sulfuricacid also depend upon numerous other factors including, but not limitedto, the amount of carbonate impurities present, the composition of thefatty acids used, the composition of the fuel oils used, the pH in theconditioner, feed rates and residence time in the scrubber.

As shown in FIG. 1, the rougher phosphate concentrate 48 is passed tode-oiling tank 50 under conditions sufficient to produce a de-oiledphosphate concentrate. A mineral acid such as sulfuric acid isintroduced into scrubber tank 50 via line 51.

The mixture of acid and rougher phosphate concentrate, as a slurry, isremoved from tank 50 via line 52 and sent into a separator vessel 54,which may be one or more V-boxes, preferably three V-boxes, althoughother type vessels may also be used. Rinse water, via means not shown,is also introduced into vessel 54.

After rinsing and separation, the rinse water containing the mineralacid is removed via line 56 for disposal 60 by means not shown.

The rinsed rougher phosphate concentrate (amine feed) 62, is removedfrom the bottom of the last V-box via line 64 and introduced into afirst cationic flotation device (second froth flotation device) 70 underconditions sufficient to further remove any inadequately de-oiledphosphate particles from the amine feed 62. Cationic collector is addedinto second flotation device 70 via line 66 in the form of an aqueousdispersion of from about 0.01 to about 0.5 pounds of cationic collectorper ton of amine feed 62. The pH of the slurry in device 70 is typicallyabout 6.0 but may be in the range of about 5.0 to about 7.0. Air, bymeans not shown, is also introduced into device 70 via line 71.

The cationic collector, when used in very small quantity, ispreferentially adsorbed by phosphate particles which are inadequatelyde-oiled. The adsorption onto silica occurs at higher collector dosage.Therefore, selective flotation of the inadequately de-oiled phosphateparticles can be obtained by using proper dosage of the cationiccollector. The floated phosphate 72 are recovered from device 70 vialine 74 and sent to phosphate concentrate storage location or area 76.The slurry 73, denuded or cleaned of inadequately de-oiled phosphateparticles is discharged from the bottom of flotation device 70 andreports to flotation device 80 via line 75. Cationic/amine collector orreagent, typically from about 0.1 to about 2.0 pounds per ton of theunderflow product from device 70 that reports to device 80, isintroduced into device 80 via line 78 under conditions sufficient toproduce an overflow product of siliceous material having very littlephosphate particles.

The cationic collector, which is positively charged, is preferentiallyadsorbed by the negatively charged silica, causing the surface of thesilica particles to become hydrophobic and to attach to air bubbles andfloat in flotation device 80. The froth is removed from the uppersection of flotation device 80 as part of the froth 79 and aretransported via line 82 to sand disposal areas (not shown). Thephosphate particles 77 remain in the water and sink. The phosphate 77,is transported from flotation device 80 via line 84 for recovery tofinal phosphate storage bin 76.

Various cationic/amine collectors known in the art can be used in thepresent invention. For example, cationic collectors useful in thepresent invention include long chain amines, amine salts including amineacetates and long chain quaternary ammonium salts. Generally, the longchain amines useful in the present invention are derived from tall oilfatty acids, tallow fatty acids, vegetable fatty acids, and long chainalcohols. More specifically, the long chain amines are preferably fattyamido amines, tallow amines, ether amines or their acetates. Further,the amines useful in the present invention may be polyfunctional.

An effective amount of a frothing agent may be added to the cationiccollector or to flotation device 70 and flotation device 80. Frothingagents useful in the present invention are known in the art, includingbut not limited to, pine oils, C₄ to C₈ alcohols, polyglycols and glycolethers. Generally the frothing agent used is less than the amount of thecationic/amine collector. Typically, the frothing agent used is anamount of 0-40 percent of the amine collector.

The flotation devices are known in the art, for example, Denverflotation devices, Wemco flotation devices and Autokumpu flotationdevices. Alternatively, column flotation devices are also useful in thepresent invention. Dual extraction columns from BeneficiationTechnologies, Inc., is one example. V-boxes or other types of boxessparged with air are also useful in the practice of the presentinvention.

As illustrated above, the present invention provides a method ofconcentrating phosphate minerals from their ores which comprises: (a)subjecting the ore as an aqueous pulp to a first froth flotationtreatment in the presence of an anionic reagent under conditionssufficient to produce a first froth overflow product of rougherphosphate concentrate and a first underflow of siliceous product; (b)subjecting the first froth overflow product of rougher phosphateconcentrate to de-oiling treatment with mineral acid under conditionssufficient to produce a de-oiled phosphate concentrate; (c) subjectingthe de-oiled phosphate concentrate to a second froth flotation treatmentin the presence of cationic collectors under conditions sufficient toproduce a second froth overflow product of a first final phosphateconcentrate and a second underflow product of phosphate particlescontaining siliceous material; (d) subjecting the second underflowproduct to a third froth flotation treatment in the presence of cationicreagents under conditions sufficient to thereby produce a third frothoverflow product of siliceous material having less phosphate particlesand a third underflow product comprising phosphate particles as a secondfinal phosphate concentrate; and (e) recovering the first and secondfinal phosphate concentrates.

The present invention is particularly useful for phosphate ore that isdifficult to de-oil. It is also useful when the carbonate content of thephosphate rock is high, because it is often difficult to maintain theacidic conditions necessary for complete de-oiling of the surface of thephosphate particles. High carbonate content requires a large excess ofsulfuric acid because the acid is consumed by the carbonates. Theincreased amount of sulfuric acid used in the de-oiling processincreases the possibility of P₂O₅ loss due to leaching of phosphaterock. This invention prevents the phosphate loss due to phosphate rockleaching. Furthermore, the present invention can be practiced withouthigh capital investment.

The method of the present invention causes the inadequately de-oiledphosphate particles to float. Specifically, the inadequately de-oiledphosphate particles are recovered as concentrate prior to silicaflotation. Accordingly, the loss of phosphate to the amine tailings isreduced. In addition, the de-oiling step becomes less critical becausede-oiling does not have to be complete. Since de-oiling does not need tobe complete the de-oiling process becomes easier. Further, the amount ofsulfuric acid used during the process is reduced, as well as, the amountof soda ash used to neutralize the sulfuric acid. If additionalflotation devices are not available, the additional in seriescationic/amine flotation circuit of the present invention can beconducted in the last V-box 54 by installing aeration systems as iswithin the skill of the art.

In fact, V-boxes or any other type of boxes sparged with air are alsouseful in the practice of the present invention. For plants that havemore than four pockets (cells) for the amine flotation circuit, theflotation of the inadequately de-oiled phosphate can be conducted in thefirst two pockets, and additional cationic collector can be added to thethird pocket (cell) to float the silica.

EXAMPLE

The following example is presented to illustrate the invention, which isnot intended to be in any way limited thereto, since numerousmodifications and variations therein will be apparent to one skilled inthe art. Actual experimental data was obtained as follows:

The results of treating the amine feed from various phosphatebeneficiation plants are shown in Table 1. Specifically, these aminefeeds were generated under regular de-oiling conditions. Subsequently,these amine feeds were subjected to an additional cationic flotationstep in accordance with the present invention. The amount of phosphateconcentrate collected from flotation of these amine feeds with thecationic/amine collector (0.2 lbs./ton feed) is shown in Table 1.

TABLE 1 Amount of Concentrate (BPL 65-66%) Feed Source % of FinalConcentrate Weight Plant A Run 1 = 3.7%; Run 2 = 3.2%; Run 3 = 4.4%; Run4 = 4.1% Plant B Run 1 = 1.5% Plant C Run 1 = 1.5%

The results shown in Table 1 clearly show the benefits of using anadditional cationic flotation step to remove the inadequately de-oiledphosphate particles from the amine feed. Additional 1.5-4.4% ofphosphate concentrate which would have been lost to the amine tailingsis recovered.

Examples of the amount of cationic collector needed to obtain a desiredrecovery and grade of phosphate floated is illustrated in FIGS. 2 and 3.FIG. 2 illustrates the relationship between cationic collector dosageand amount floated, and FIG. 3 illustrates the relationship betweencationic collector dosage and float grade. FIG. 3 shows that increasesilica flotation occurs when cationic collector dosage exceeds 0.2 lbs.per ton of amine feed. The actual amounts of collector needed depends onthe feed, the molecular structure and composition of the collector,slime content of the water, etc.

This invention is clearly new and useful. Moreover, it was not obviousto those of ordinary skill in this art at the time it was made. Sincecertain changes may be made in the foregoing description withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description shall be interpreted asillustrative and not in a limiting sense.

Further, it is understood that alternative embodiments from thatdepicted in FIG. 1 are useful in the present invention. Those skilled inthe art recognize that other structures and features may be present inthe beneficiation flow sheet of the present invention. For example, somebeneficiation plants have distribution boxes at various positions in theflow sheet (not shown). Distribution boxes may be used for the additionof reagents.

It should be understood that the preceding is only a description of oneembodiment of this invention and that numerous changes to the disclosedembodiment can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. The precedingdescription, therefore, is not meant to limit the scope of theinvention. Rather, the scope of the invention is to be determined onlyby the appended claims and their equivalents.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Now that the invention has been described,

What is claimed is:
 1. A method of concentrating phosphate minerals fromtheir ores comprising: subjecting the ore as an aqueous pulp to a firstfroth flotation treatment in the presence of an anionic collector underconditions sufficient to produce a first froth overflow product ofrougher phosphate concentrate and a first underflow product of siliceousmaterial; subjecting the first froth overflow product of rougherphosphate concentrate to de-oiling treatment with mineral acid underconditions sufficient to produce a de-oiled phosphate concentrate;subjecting the de-oiled phosphate concentrate to a second frothflotation treatment in the presence of cationic collectors underconditions sufficient to produce a second froth overflow product of afirst final phosphate concentrate and a second underflow product ofphosphate particles containing siliceous material; subjecting the secondunderflow product to a third froth flotation treatment in the presenceof cationic collectors under conditions sufficient to produce a thirdfroth overflow product of siliceous material having less phosphateparticles and a third underflow product of a second final phosphateconcentrate; and recovering the first and second final phosphateconcentrate.
 2. The method according to claim 1, wherein the cationiccollectors are selected from the group consisting of long chain amines,amine salts, long chain quaternary ammonium salt, and mixtures thereof.3. The method according to claim 1, where a frothing agent is added tothe second froth flotation treatment.
 4. The method according to claim3, wherein the frothing agent is selected from the group consisting ofpine oils, c₄-c₈ alcohols, polyglycols, and glycol ethers.
 5. The methodaccording to claim 1, wherein the conditions sufficient to produce thefirst final phosphate concentrate includes an amount of cationiccollector of from about 0.01 to about 0.5 pounds of collector per ton ofthe de-oiled phosphate concentrate.
 6. The method according to claim 1,wherein the conditions sufficient to produce the second final phosphateconcentrate include an amount of cationic collector of from about 0.1 toabout 2 pounds of the collector per ton of the second underflow productof phosphate particles containing siliceous material.
 7. The methodaccording to claim 1, wherein the conditions sufficient to produce thefirst final phosphate concentrate include the presence of a frothingagent.
 8. The method according to claim 7, wherein the frothing agent isselected from the group consisting of pine oils, c₄-c₈ alcohols,polyglycols, and glycol ethers.
 9. The method according to claim 1,wherein the conditions sufficient to produce the second final phosphateconcentrate include the presence of a frothing agent.
 10. The methodaccording to claim 9, wherein the frothing agent is selected from thegroup consisting of pine oils, c₄-c₈ alcohols, polyglycols, and glycolethers.
 11. The method according to claim 1, wherein the mineral acid issulfuric acid.